A replicated study between 1964 and 1975 in six wetland sites in Texas, USA (McCamant & Bolen 1979), found that black-bellied whistling ducks Dendrocygna autumnalis used an average of 81% of nest boxes erected in trees. On average, 52 nest boxes were available each year and were monitored an average of 14 times a year. A total of 778 clutches were laid over the study period, with 40% incubated and 75% of these hatching at least one egg successfully (210 nests, 28% of all nests). Sixty three percent of eggs in successful nests hatched, compared with a population average of 20%.